Method for Transmission of Unicast Control in Broadcast/Multicast Transmission Time Intervals

ABSTRACT

Embodiments of the invention provide methods for maximizing the bandwidth utilization in the uplink of a communication system supporting time division multiplexing between unicast and multicast/broadcast communication modes during transmission time intervals in the downlink of a communication system. This is accomplished by multiplexing at least unicast control signaling for UL scheduling assignments in TTIs supporting the multicast/broadcast communication mode. Moreover, multiplexing of unicast control signaling can also be accomplished by splitting a symbol of the multicast/broadcast TTI into two shorter symbols with the first of these two shorter symbols carrying at least unicast control signaling and the second of these shorter symbols carrying multicast/broadcast signaling.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and incorporates by reference U.S.Provisional Application No. 60/733,675, filed Nov. 4, 2005, entitled“Method for Transmission of Unicast Control/Data in Broadcast TTI's”,Aris Papasakellariou, Timothy Schmidl, Eko Onggosanusi, Anand Dabakinventors.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Embodiments of the invention are directed, in general, to communicationsystems and, more specifically, to enabling unicast signaling from userequipments UEs to a serving base station BS during transmission timeintervals that the base station transmits multicast/broadcast signalingto user equipments UEs.

The global market for both voice and data communication servicescontinues to grow as does users of the systems which deliver thoseservices. As communication systems evolve, system design has becomeincreasingly demanding in relation to equipment and performancerequirements. Future generations of communication systems, will berequired to provide high quality high transmission rate data services inaddition to high quality voice services. Orthogonal Frequency DivisionMultiplexing (OFDM) is a technique that will allow for high speed voiceand data communication services.

Orthogonal Frequency Division Multiplexing (OFDM) is based on thewell-known technique of Frequency Division Multiplexing (FDM). OFDMtechnique relies on the orthogonality properties of the fast Fouriertransform (FFT) and the inverse fast Fourier transform (IFFT) toeliminate interference between carriers. At the transmitter, the precisesetting of the carrier frequencies is performed by the IFFT. The data isencoded into constellation points by multiple (one for each carrier)constellation encoders. The complex values of the constellation encoderoutputs are the inputs to the IFFT. For wireless transmission, theoutputs of the IFFT are converted to an analog waveform, up-converted toa radio frequency, amplified, and transmitted. At the receiver, thereverse process is performed. The received signal (input signal) isamplified, down converted to a band suitable for analog to digitalconversion, digitized, and processed by a FFT to recover the carriers.The multiple carriers are then demodulated in multiple constellationdecoders (one for each carrier), recovering the original data. Since anIFFT is used to combine the carriers at the transmitter and acorresponding FFT is used to separate the carriers at the receiver, theprocess has potentially zero inter-carrier interference such as when thesub-carriers are separated in frequency by an amount larger than themaximum expected Doppler shift.

FIG. 1 is a diagram illustrative of the Frequency 103—Time 101Representation 100 of an OFDM Signal. In FDM different streams ofinformation are mapped onto separate parallel frequency channels 140.Each FDM channel is separated from the others by a frequency guard bandto reduce interference between adjacent channels.

The OFDM technique differs from traditional FDM in the followinginterrelated ways:

-   -   1. multiple carriers (called sub-carriers 150) carry the        information stream;    -   2. the sub-carriers 150 are orthogonal to each other; and    -   3. a Cyclic Prefix (CP) 110 (also known as guard interval) is        added to each symbol 120 to combat the channel delay spread and        avoid OFDM inter-symbol interference (ISI).

The data/information carried by each sub-carrier 150 may be user data ofmany forms, including text, voice, video, and the like. In addition, thedata includes control data, a particular type of which is discussedbelow. As a result of the orthogonality, ideally each receiving elementtuned to a given sub-carrier does not perceive any of the signalscommunicated at any other of the sub-carriers. Given this aspect,various benefits arise. For example, OFDM is able to use orthogonalsub-carriers and, as a result, thorough use is made of the overall OFDMspectrum. As another example, in many wireless systems, the sametransmitted signal arrives at the receiver at different times havingtraveled different lengths due to reflections in the channel between thetransmitter and receiver. Each different arrival of the sameoriginally-transmitted signal is typically referred to as a multi-path.Typically, multi-paths interfere with one another, which is sometimesreferred to as InterSymbol Interference (ISI) because each path includestransmitted data referred to as symbols. Nonetheless, the orthogonalityimplemented by OFDM with a CP considerably reduces or eliminates ISIand, as a result, often a less complex receiver structure, such as onewithout an equalizer (one-tap “equalizer” is used), may be implementedin an OFDM system.

The Cyclic Prefix (CP) (also referred to as guard interval) is added toeach symbol to combat the channel delay spread and avoid ISI. FIG. 2 isa diagram illustrative of using CP to eliminate ISI and performfrequency domain equalization. Blocks 200 each comprising cyclic prefix(CP) 210 coupled to data symbols 220 to perform frequency domainequalization. OFDM typically allows the application of simple, 1-tap,frequency domain equalization (FDE) through the use of a CP 210 at everyFFT processing block 200 to suppress multi-path interference. Two blocksare shown for drawing convenience. CP 210 eliminates inter-data-blockinterference and multi-access interference using Frequency DivisionMultiple Access (FDMA).

Since orthogonality is typically guaranteed between overlappingsub-carriers and between consecutive OFDM symbols in the presence oftime/frequency dispersive channels, the data symbol density in thetime-frequency plane can be maximized and high data rates can be veryefficiently achieved for high Signal-to-Interference and Noise Ratios(SINR).

FIG. 3 is a diagram illustrative of CP Insertion. A number of samples istypically inserted between useful OFDM symbols 320 (guard interval) tocombat OFDM ISI induced by channel dispersion, assist receiversynchronization, and aid spectral shaping. The guard interval 310 istypically a prefix that is inserted 350 at the beginning of the usefulOFDM symbol (OFDM symbol without the CP) 320. The CP duration 315 shouldbe sufficient to cover most of the delay-spread energy of a radiochannel impulse response. It should also be as small as possible sinceit represents overhead and reduces OFDM efficiency. Prefix 310 isgenerated using a last block of samples 340 from the useful OFDM symbol330 and is therefore a cyclic extension to the OFDM symbol (cyclicprefix).

When the channel delay spread exceeds the CP duration 315, the energycontained in the ISI should be much smaller than the useful OFDM symbolenergy and therefore, the OFDM symbol duration 325 should be much largerthan the channel delay spread. However, the OFDM symbol duration 325should be smaller than the minimum channel coherence time in order tomaintain the OFDM ability to combat fast temporal fading. Otherwise, thechannel may not always be constant over the OFDM symbol and this mayresult in inter-sub-carrier orthogonality loss in fast fading channels.Since the channel coherence time is inversely proportional to themaximum Doppler shift (time-frequency duality), this implies that thesymbol duration should be much smaller than the inverse of the maximumDoppler shift.

The large number of OFDM sub-carriers makes the bandwidth of individualsub-carriers small relative to the total signal bandwidth. With anadequate number of sub-carriers, the inter-carrier spacing is muchnarrower than the channel coherence bandwidth. Since the channelcoherence bandwidth is inversely proportional to the channel delayspread, the sub-carrier separation is generally designed to be muchsmaller that the inverse of the channel coherence time. Then, the fadingon each sub-carrier appears flat in frequency and this enables 1-tapfrequency equalization, use of high order modulation, and effectiveutilization of multiple transmitter and receiver antenna techniques suchas Multiple Input/Multiple Output (MIMO). Therefore, OFDM effectivelyconverts a frequency-selective channel into a parallel collection offrequency flat sub-channels and enables a very simple receiver.Moreover, in order to combat Doppler effects, the inter-carrier spacingshould be much larger than the maximum Doppler shift.

By assigning transmission to various simultaneously scheduled UEs indifferent RBs, the Node B scheduler can provide intra-cell orthogonalityamong the various transmitted signals. Moreover, for each individualsignal, the presence of the cyclic prefix provides protection frommultipath propagation and maintains in this manner the signalorthogonality.

Each scheduled UE is informed of the scheduling assignment through thedownlink (DL) control channel. The scheduling assignment can be for asignal transmission from the Node B and reception by a UE (downlinkscheduling assignment) or for a signal transmission from the UE andreception at the Node B (uplink scheduling assignment). The controlchannel typically carries the scheduled UE identities (IDs), RBassignment information, the MCS used to transmit the data, the transportblock size, and hybrid ARQ (HARQ) information relating to possible datapacket re-transmissions. The control channel may optionally carryadditional information such as for a multi-input multi-output (MIMO)transmission scheme. A scheduling assignment may relate either to datatransmission from the Node B to a UE (downlink of a communicationsystem) or to data transmission from a UE to the Node B (uplink of acommunication system).

DL communication may involve dedicated communication from one or moreserving Node Bs to multiple UEs in a unicast mode. This mode impliesthat the transmitted data signal carries information that is specific toa single UE. DL communication may also involve multicast/broadcastcommunication from one or more serving Node Bs to multiple UEs in amulticast/broadcast mode. This mode implies that the transmitted datasignal carries information that is intended to multiple UEs (commoninformation data content). For example, a unicast transmission may be afile download by a UE while broadcast/multicast transmission may be thebroadcasting of news.

When the available communication bandwidth is not excessively large, apreferable method to multiplex the unicast and multicast/broadcast modesof communication is through time division multiplexing (TDM). With TDM,unicast communication exists during certain transmission time intervals(TTIs) of a frame while multicast/broadcast communication may commenceduring the remaining TTIs.

In TTIs supporting the multicast/broadcast mode, no unicastcommunication exists in the DL. However, it is still possible totransmit unicast data and associated control signaling in the uplink(UL) of the communication system. Otherwise, substantial bandwidthresources can be wasted in the UL.

To enable scheduling of data transmissions in the UL, a correspondingcontrol channel carrying the respective scheduling assignments forunicast communication needs to be transmitted during multicast/broadcastTTIs.

Thus, there is a need to maximize the spectrum use in the uplink of acommunication system employing time division multiplexing of unicast andmulticast/broadcast communication modes in the downlink.

There is another need to multiplex unicast control signalling forscheduling assignments of uplink data signal transmissions in TTIssupporting the multicast/broadcast communication mode.

There is another need to minimize the overhead of unicast controlsignalling in TTIs supporting the multicast/broadcast communicationmode.

SUMMARY

Embodiments of the invention provide a method to maximize the bandwidthutilization in the uplink (UL) of a communication system supporting timedivision multiplexing (TDM) between unicast and multicast/broadcastcommunication modes during transmission time intervals (TTIs) in thedownlink (DL) of a communication system. This is accomplished bymultiplexing at least unicast control signaling for UL schedulingassignments in TTIs supporting the multicast/broadcast communicationmode.

As the unicast control signaling for UL scheduling assignmentsconstitutes overhead in TTIs supporting the multicast/broadcastcommunication mode, the overall signaling related to this overhead needsto be minimized. This minimization primarily concerns the transmissionof pilot signals (or reference signals) associated with the demodulationof the unicast control signaling at user equipments (UEs).

The multicast/broadcast TTI is assumed to comprise of symbols.Multiplexing of unicast control signaling can also be accomplished bysplitting a symbol of the multicast/broadcast TTI into two shortersymbols with the first of these two shorter symbols carrying at leastunicast control signaling and the second of these two shorter symbolscarrying multicast/broadcast signaling.

These and other features and advantages will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosure and the advantagesthereof, reference is now made to the following brief description, takenin connection with the accompanying drawings and detailed description,wherein like reference numerals represent like parts.

FIG. 1 is a diagram illustrative of the Frequency-Time Representation ofan OFDM Signal;

FIG. 2 is a diagram illustrative of using cyclic prefix (CP) toeliminate ISI and perform frequency domain equalization;

FIG. 3 is a diagram illustrative of Cyclic Prefix (CP) Insertion

FIG. 4 is a diagram illustrative of unicast and multicast/broadcasttransmission time intervals (TTIs);

FIG. 5 is a diagram illustrative of shared unicast andmulticast/broadcast multiplexing in the first OFDM symbol of amulticast/broadcast transmission time interval (TTI);

FIG. 6 is a diagram illustrative of unicast multiplexing in the firstOFDM symbol of a multicast/broadcast transmission time interval (TTI);

FIG. 7 shows unicast and multicast/broadcast sub-carrier multiplexing inthe first OFDM symbol of a multicast/broadcast transmission timeinterval (TTI); and

FIG. 8 shows sub-carrier multiplexing of unicast signals in the firstOFDM symbol of a multicast/broadcast transmission time interval (TTI).

DETAILED DESCRIPTION

It should be understood at the outset that although an exemplaryimplementation of one embodiment of the disclosure is illustrated below,the system may be implemented using any number of techniques, whethercurrently known or in existence. The disclosure should in no way belimited to the exemplary implementations, drawings, and techniquesillustrated below, including the exemplary design and implementationillustrated and described herein, but may be modified within the scopeof the appended claims along with their full scope of equivalents.

Embodiments of the invention address the problem of optimum utilizationof the frequency spectrum available for uplink (UL) data packettransmissions in OFDMA-based networks, including variants of the OFDMAtransmission method such as the single-carrier FDMA (SC-FDMA)transmission method, supporting time division multiplexing (TDM) betweenunicast and multicast/broadcast communication modes. The unicastcommunication mode refers to dedicated communication from one or morebase stations (also referred to as Node Bs) to a single user equipment(UE) or the reverse (dedicated communication from a UE to one or moreNode Bs). The multicast/broadcast communication mode refers tocommunication from one or more Node Bs to potentially and typicallymultiple UEs. In the preferred embodiment of the invention, DL controlsignalling providing scheduling assignments to UEs for UL datatransmissions during multicast/broadcast TTIs (unicast control) ismultiplexed in these TTIs.

Embodiments of the invention also address the minimization of theoverhead associated with the multiplexing of unicast control inmulticast/broadcast TTIs. As unicast control is assumed to be alreadyoptimized for spectral efficiency, the minimization concerns the optimummultiplexing method in order to minimize the signaling overheadassociated with the demodulation of unicast control signaling at UEs. Inparticular this signaling overhead refers to the required unicast pilot(reference) signals.

FIG. 4 shows an exemplary structure of a unicast and broadcast/multicasttransmission time interval (TTI) having the same duration 405. Theunicast TTI 410, has a “short” cyclic prefix (CP) 420 and comprises ofseven OFDM symbols 430. The multicast/broadcast TTI 450, has a “long” CP460 and comprises of six OFDM symbols 470. Because unicast transmissionsare associated with communication between a UE and one or very few NodeBs, the propagation delay and multi-path delay spread are typically muchsmaller than the corresponding ones for multicast/broadcasttransmissions for which the same signal is transmitted by multiple NodeBs which may have substantial geographic separation. For this reason,unicast OFDM symbols are associated with a shorter CP and a shorterduration than multicast/broadcast OFDM symbols. Nevertheless, theinvention does not preclude unicast communications in very large cellswhere the aforementioned delays are similar to those experienced bymulticast/broadcast communications. Then, the two CPs may have similaror even the same value in which case the number of OFDM symbols is thesame for both unicast and multicast/broadcast communication modes (notshown).

FIG. 5 shows one embodiment of the invention for the multiplexing ofunicast control signaling in a multicast/broadcast TTI in the DL of acommunication system. TDM is assumed for the unicast andmulticast/broadcast TTIs. Part of the unicast control information and apilot signal (also known as reference signal) 510 associated with aunicast TTI 520, are multiplexed with broadcast signaling 540 in thefirst OFDM symbol of the multicast/broadcast TTI 550. The unicastcontrol information is typically associated with scheduling assignmentsrelated to both transmissions from a serving Node B to UEs (DLscheduling assignments) and to a serving Node B from UEs (UL schedulingassignments). Since only UL scheduling assignments are assumed possibleduring multicast/broadcast TTIs, only the corresponding unicast controlsignaling is multiplexed in a multicast/broadcast TTI. For the remainingof this invention, the multiplexing of unicast control signaling inmulticast/broadcast TTIs will refer exclusively to UL schedulingassignments for unicast UL transmissions from UEs (that is, DLscheduling assignments or other control information for unicast DLcommunication are not included). It should be noted that, in addition toscheduling assignments, the UL unicast control may also provide the UEstiming control and power control information in order for the UEs toperform respective time adjustments and power adjustments to thecorresponding UL signal transmissions.

In addition to the UL scheduling assignments, unicast pilots may alsohave to be multiplexed in order to ensure sufficiently reliable channelestimation for the demodulation of the unicast control channel inmulticast/broadcast TTIs. Alternatively, if unicast pilots in theunicast TTI 520 are placed in the latter OFDM symbols of that TTI, theirtime separation from the first OFDM symbol of the multicast/broadcastTTI 550 may be small enough to provide for sufficiently accurate channelestimation even at very high UE velocities, thereby not necessitatingthe inclusion of unicast pilots in the first symbol of themulticast/broadcast TTI. Notice however that this may imply theinclusion of unicast pilots at a later OFDM symbol of themulticast/broadcast TTI to facilitate channel estimation in the ensuingunicast TTI 570.

The multicast/broadcast signaling 540 may include broadcast pilots,broadcast control, or broadcast data. It may be possible to multiplexboth unicast control, and probably unicast pilots, with broadcastsignaling in the same OFDM symbol of a multicast/broadcast TTI if themaximum possible size of unicast control is smaller than thecorresponding number of sub-carriers in that OFDM symbol. Obviously, inorder for unicast pilots to be also accommodated, the unicast controlinformation should be substantially smaller than the aforementionednumber of sub-carriers, which may imply that only a small number of UEscan receive UL scheduling assignments.

If the unicast control signaling is too large to allow additionalmultiplexing of multicast/broadcast signaling in the same OFDM symbol ofa multicast/broadcast TTI, only unicast signaling may occupy that OFDMsymbol. The unicast signaling includes unicast control and can alsoinclude unicast pilots. This is depicted in FIG. 6. TDM is again assumedbetween unicast TTIs 620 and multicast TTIs 630. In this embodiment ofthe invention, the first OFDM symbol of the multicast/broadcast TTIcontains only unicast signaling 650 (unicast control and probablyunicast pilots) and does not contain any broadcast signaling.

FIG. 7 provides a more detailed depiction of the shared unicast andmulticast/broadcast multiplexing 540. The available frequencysub-carriers 710 in the first OFDM symbol of the multicast/broadcast TTIare partitioned into unicast sub-carriers 730 and multicast/broadcastsub-carriers 740. The remaining of the multicast/broadcast TTI isassumed to be assigned to multicast/broadcast symbols 750. The unicastsub-carriers may include unicast control sub-carriers (for example, twoout of three unicast sub-carriers) and unicast pilot sub-carriers (forexample, one out of three unicast sub-carriers). Alternatively, theunicast sub-carriers may exclusively carry unicast control. Aspreviously mentioned, the multicast/broadcast sub-carriers may carrycorresponding control, pilot, or data signaling.

FIG. 8 provides a more detailed depiction of the unicast multiplexing650. The available frequency sub-carriers 810 in the first OFDM symbolof the multicast/broadcast TTI are partitioned into unicast controlsub-carriers 830 and unicast pilot sub-carriers 840. The remaining ofthe multicast/broadcast TTI is assumed to be assigned tomulticast/broadcast symbols 850.

As shown in FIGS. 5-8, the preferred embodiment considers that theunicast control is multiplexed in the first OFDM symbol of themulticast/broadcast TTI. Moreover, additional symbols at the beginningof the multicast/broadcast TTI may be used, especially if themulticast/unicast TTI comprises of more than the six OFDM symbols shownin FIGS. 5-8 and in FIG. 4. For example, for a multicast/broadcast TTIcomprising of 12 OFDM symbols, unicast control may be spread over thefirst six OFDM symbols. In general, having unicast control signalingtransmitted at the beginning of the multicast/broadcast TTIs simplymeans that the unicast control signaling terminates prior to thetermination of a multicast/broadcast TTI.

There are multiple reasons for the transmission of the unicast controlin the multicast/broadcast TTI with minimum latency and with priority tothe multicast/broadcast signal transmission.

One reason is that UL scheduling assignments may be based on channelquality indicators (CQI) provided by UEs to the Node B scheduler severalTTIs before a reference multicast/unicast TTI. The CQI for UL schedulingof a UE is typically implicitly provided to the Node B through thetransmission by that UE of a pilot signal occupying the entirescheduling bandwidth. The Node B computes the UL channel the signaltransmission from that UE will experience based on the previous pilotsignal.

The larger the latency in receiving the UL scheduling assignmentsthrough the unicast control, the later the UL data transmission will be,and the more inaccurate the CQI on which the Node B scheduling was basedwill become relative to the actual channel the signal transmitted from aUE with an UL scheduling assignment will experience. Such inaccuracies(mismatches) between the UL channel indicated by the CQI for the Node Bto perform UL scheduling and the actual UL channel experienced duringthe signal transmission can cause significant degradation in theachievable throughput. Therefore, the unicast control channel should bemultiplexed in multicast/broadcast TTIs so that it can be received withminimum latency. This implies transmission of unicast control in thebeginning of the multicast/broadcast TTI.

Another reason for multiplexing the unicast control in the beginning ofa multicast/broadcast TTI is to minimize the unicast pilot overhead forthe demodulation of that unicast control. If the unicast control wasdistributed throughout the multicast/broadcast TTI, then multipleunicast pilots would also be required to be distributed throughout thatTTI, thereby increasing the corresponding unicast pilot overhead. Thisis because, especially at very high UE velocities, time interpolationbetween unicast pilots located at various OFDM symbols of themulticast/broadcast TTI may not be possible.

Another reason for multiplexing the unicast control in the beginning ofa multicast/broadcast TTI is to minimize buffering and latencyrequirements at the UE receiver for processing the unicast control.

Another reason for multiplexing the unicast control in the beginning ofa multicast/broadcast TTI is to enable a “micro-sleep” mode for UEs.With micro-sleep, UEs that did not receive an UL scheduling assignmentduring the multicast/broadcast TTI, and do not receivemulticast/broadcast information, may shut down parts of theirtransmitter and receiver chains and turn them back on again in time toreceive the next TTI and its control information. This can enable UEs tobe more power efficient due to the associated power savings.

In addition to multiplexing unicast control and possibly unicast pilotin the first OFDM symbols of a multicast/broadcast TTI, this first OFDMsymbol may instead be split into two (shorter) OFDM symbols. Forexample, each of these two OFDM symbols may having half the duration ofthe original OFDM symbol with the first of these two symbols exclusivelycarrying unicast signals and the second exclusively carrying multicastsignals. Although more transparent, this option has the slightdisadvantage of increasing the CP overhead as an additional unicast(short) CP is required but it may decrease the overall unicast overheadin multicast/broadcast TTIs. For example, a 1024 point IFFT is used toform multicast/broadcast OFDM symbols, then a 512 point FFT could beused for the OFDM symbol carrying unicast signals.

While several embodiments have been provided in the disclosure, itshould be understood that the disclosed systems and methods may beembodied in many other specific forms without departing from the spiritor scope of the disclosure. The examples are to be considered asillustrative and not restrictive, and the intention is not to be limitedto the details given herein, but may be modified within the scope of theappended claims along with their full scope of equivalents. For example,the various elements or components may be combined or integrated inanother system or certain features may be omitted, or not implemented.

Also, techniques, systems, subsystems and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the disclosure. Other itemsshown or discussed as directly coupled or communicating with each othermay be coupled through some interface or device, such that the items mayno longer be considered directly coupled to each other but may still beindirectly coupled and in communication, whether electrically,mechanically, or otherwise with one another. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

1. In a communication system supporting a unicast communication mode anda multicast/broadcast communication mode wherein unicast transmissiontime intervals (TTIs) are multiplexed with multicast/broadcast TTIsthrough time division multiplexing, a method to perform signaltransmissions from user equipments (UEs) to a serving Node B during saidmulticast/broadcast transmission time intervals, said method comprising:transmitting from said Node B unicast signaling in saidmulticast/broadcast transmission time intervals said unicast signalingcomprising at least unicast control signaling; and receiving saidunicast control signaling at an at least one UE.
 2. The method of claim1, wherein said at least one UE transmits a signal in response to saidreceiving said unicast control signaling.
 3. The method of claim 1,wherein said unicast control signaling is transmitted with priority tomulticast/broadcast signaling at the beginning of saidmulticast/broadcast TTI.
 4. The method of claim 1, wherein said unicastcontrol provides scheduling assignments for data signal transmissionfrom at least one of said UEs.
 5. The method of claim 1, wherein saidunicast control provides timing control or power control information toat least one of said UEs.
 6. The method of claim 5, wherein said atleast one of said UEs adjusts its signal transmission power or itssignal transmission timing in response to said timing control or powercontrol information, respectively.
 7. The method of claim 1, whereinsaid unicast signaling further comprises of unicast pilot signaling. 8.The method of claim 7, wherein said unicast pilot signaling istransmitted with priority to multicast/broadcast signaling at thebeginning of said multicast/broadcast TTI.
 9. The method of claim 1,wherein said multicast/broadcast TTI comprises of symbols and saidunicast signaling is multiplexed with multicast/broadcast signaling inthe same symbol.
 10. The method of claim 1, wherein saidmulticast/broadcast TTI comprises of symbols and said unicast signalingand multicast/broadcast signaling are multiplexed in different symbols.11. The method of claim 1, wherein said communication system employs theOFDMA transmission method.
 12. In a communication system supporting aunicast communication mode and a multicast/broadcast communication modewherein unicast transmission time intervals (TTIs) are multiplexed withmulticast/broadcast TTIs through time division multiplexing, saidmulticast/broadcast TTIs further comprising of symbols, a method toperform signal transmissions from user equipments (UEs) to a servingNode B during said multicast/broadcast transmission time intervalscomprising the steps of: dividing at least one of said symbols of saidmulticast/broadcast TTI into two shorter symbols; transmitting unicastsignaling comprising of at least unicast control signaling in a first ofsaid two shorter symbols; and transmitting multicast/broadcast signalingin a second of said two shorter symbols.
 13. The method of claim 12,wherein said at least one symbol is located at the beginning of saidmulticast/broadcast TTI.
 14. The method of claim 12, wherein said afirst of said two shorter symbols is the first of the said two shortersymbols.
 15. The method of claim 12, wherein said unicast signalingfurther comprises of unicast pilot signaling.
 16. The method of claim12, wherein said communication system employs the OFDMA transmissionmethod.
 17. In a communication system supporting a unicast communicationmode and a multicast/broadcast communication mode wherein unicasttransmission time intervals (TTIs) are multiplexed withmulticast/broadcast TTIs through time division multiplexing, a method toperform signal transmissions from user equipments (UEs) to a servingNode B during said multicast/broadcast transmission time intervals, saidmethod comprising: receiving unicast signaling in saidmulticast/broadcast transmission time intervals said unicast signalingcomprising at least unicast control signaling; and transmitting a signalin response to said receiving said unicast control signaling.
 18. Themethod of claim 17, wherein said unicast control signaling is receivedat the beginning of said multicast/broadcast TTIs.
 19. The method ofclaim 17, wherein said unicast control provides scheduling assignmentsfor data signal transmission from at least one of said UEs.
 20. Themethod of claim 17, wherein said unicast control provides timing controlor power control information to at least one of said UEs.
 21. The methodof claim 20, wherein said at least one of said UEs adjusts its signaltransmission power or its signal transmission timing in response to saidtiming control or power control information, respectively.
 22. Themethod of claim 17, wherein said unicast signaling further comprisesunicast pilot signaling.
 23. The method of claim 17, wherein saidcommunication system employs the OFDMA transmission method.